Screwable foundations are inserted in various ways and are also driven into the ground with screw-in tools of mechanical type. In order to be nevertheless able to drive the screwable foundations into the ground reliably for varying soil conditions, i.e. in particular when stones are situated in the screw-in path of the screwable foundation, the corresponding screwable foundations have been equipped with hardened tips or with chisel-like additional tools, which are guided in the interior of the screwable foundation and serve for the destruction of the stone, as it were, at the leading edge during the driving of the screwable foundation.
In contrast, strike-in sleeves are known, which are merely struck or respectively driven into the ground by a striking tool. Whereas in the case of strike-in sleeves only one strike-in apparatus is present, i.e. a screwing-in prohibits itself, because the strike-in sleeves have webs, constructed in longitudinal or respectively strike-in direction, to secure against rotation, the screwable foundations have thread-like webs arranged on their outer contour, so that they can be screwed in level into the ground. Screwable foundations are therefore not suitable for striking in.
During screwing in, for the purpose of a reliable anchoring, the screw-in sleeve, i.e. the screwable foundation with the webs, is to rotate into the ground, but is not to loosen it substantially. Depending on the soil conditions, therefore different web heights have been developed. In order to be able to also reliably drive screwable foundations into soils which are very hard or which have stones as obstacles for the driving of the screwable foundations, screwable foundations with open tips have been developed, in which an additional percussion bit is introduced into the screwable foundations, complicating the entire driving system, so that during the screwing in by means of a striking movement onto the bit, stones in the soil ahead of the screwable foundation can be broken or disintegrated if applicable. The striking movement of the bit takes place here independently of the rotary movement of the screwable foundation.
Owing to the fact that screwable foundations are screwed into the ground and, in order to guarantee a reliable anchoring, are not to be loosened during the screwing-in process, it prohibits itself to use rotary tools and striking tools together for the driving of screwable foundations.
Such combinations are only known for pile-driving devices, which are also designated as drill hammers. These devices serve for the production of tubular earth bores and are similar in basic structure to those such as are used for percussion drill devices for example for the drilling of hard concrete and are generally known (see DE 3911467 C2).
The fundamental sequence in the use of such drill hammers would mean that firstly pre-drilling would be carried out, then a drill would have to be removed from the produced borehole in order to subsequently be able to screw in a foundation, if applicable. The pre-drilling and production of a borehole for the driving of a screwable foundation is, however, disadvantageous especially also because if applicable it can then not be ensured that the screwable foundation is reliably anchored, and because, moreover, a pre-drilled hole has in fact been produced for the screwable foundation, but it is not to be ruled out that a stony soil condition offers considerable resistance to the penetration of the screw helixes of the screwable foundation, so that on screwing in even with a pre-drilled hole if applicable the screwable foundation which is to be driven could be damaged or even destroyed.
In addition, from DE 36 17 025 A1 for prefabricated concrete piles it is known to drive these into the ground with the exerting of an axial speed of advance and simultaneous rotation about their longitudinal axis. In an embodiment, the speed of advance and the rotational movement are synchronized according to the pitch of the helical rib arrangement. Firstly, here, the rotational speed is regulated as a function of the actual distance covered, until some turns of the rib have caught in the subsoil and the axial force necessary for the displacing of the ground can be provided by pure further rotation of the concrete pile owing to the support of the rib. Then primarily the rotational speed is set according to the desired speed of advance.